To oczywisty błąd.

Here to is a very common Polish word used in sentences like To oczywisty błąd to mean something like this, that, or it in English.

In this pattern, to introduces an identification:

• To problem. = That/This is a problem.
• To mój brat. = This/That is my brother.

So in your sentence, to points to some situation, action, statement, or thing already understood from context and says what it is.

Because in this kind of sentence, Polish often leaves out jest (is).

So:

• To oczywisty błąd.
• To jest oczywisty błąd.

Both are correct.

This happens especially in simple identifying sentences with to. English needs is, but Polish often does not.

Yes. To jest oczywisty błąd is completely correct.

The version without jest is a little more compact and very natural:

• To oczywisty błąd.

The version with jest is also natural:

• To jest oczywisty błąd.

As a learner, you can safely use either one.

Because Polish does not have articles like a, an, or the.

So błąd can mean:

• a mistake
• the mistake

The exact meaning depends on context. In this sentence, English normally uses an:

• an obvious mistake

But Polish simply says:

• oczywisty błąd

Because the adjective has to agree with the noun it describes.

The noun błąd is:

• masculine
• singular
• nominative

So the adjective must also be masculine singular nominative:

• oczywisty błąd

Compare:

• oczywista pomyłka = feminine
• oczywiste przeoczenie = neuter
• oczywiste błędy = plural

This agreement is a basic feature of Polish grammar.

Because in this type of sentence with to, Polish normally uses the nominative:

• To błąd.
• To problem.
• To prawda.

So here the full noun phrase is nominative:

• oczywisty błąd

This can be confusing because learners often know sentences like:

• Jan jest nauczycielem.

There, nauczycielem is instrumental. But after to in an identifying sentence, nominative is the normal choice.

The most natural order here is:

• To oczywisty błąd.

That is the normal, neutral version.

You may sometimes see different orders, but they usually sound more marked, literary, or emphatic. For example:

• To błąd oczywisty. — possible, but more stylistically marked

For everyday Polish, To oczywisty błąd is the best model to copy.

A few parts are especially important:

• cz in oczywisty sounds roughly like English ch, but harder and farther back.
• y has no exact English equivalent. It is not the same as English ee.
• ł in błąd sounds like English w.
• ą in błąd is nasal; before d, it is often heard approximately like on.
• Final d is devoiced, so it sounds closer to t at the end.

A rough English-friendly approximation would be:

• to o-chy-VIS-ty bwont

That is only approximate, but it helps.

The stress is on the second-to-last syllable of oczywisty:

• o-czy-WIS-ty

Yes. To can also introduce plural identification.

For example:

• To oczywiste błędy. = These/Those are obvious mistakes.
• To są oczywiste błędy. = same idea, with są (are) added

So to does not change just because the following noun is plural.

It is neutral and very natural. You can use it in everyday speech, writing, discussion, and argument.

It sounds direct and clear. If you want a slightly fuller version, you can say:

• To jest oczywisty błąd.

But the shorter version is not slangy or incorrect. It is standard Polish.